Speakerphones have gained widespread acceptance in the market place, and are used by a majority of businesses to facilitate communications. Speakerphones have also become prominent in many consumer markets where they are used as "hands free" phones. However, speakerphones are primarily used in land line communication systems where a regular telephone speaker circuit is replaced by a more powerful one, and a high sensitivity microphone and accompanying circuit is used instead of a conventional circuit. The more powerful speaker and more sensitive microphone are typically used in conjunction with some means for mitigating when these respective components are active. In a typical speakerphone, if the speaker is playing audio signals, if the microphone is not disabled, then the person or persons to which the user of the speakerphone is talking will hear themselves, resulting in undesirable feedback. There are some very expensive speakerphones that include sophisticated echo and feedback cancellation circuits, but the expense of such devices is quite prohibitive. Additionally, there are cordless speakerphones available, but these tend to be simply an extension of cordless phones.
As of the present time, few manufactures have successfully designed a mobile speakerphone, despite the obvious desirability of such a device. That is, a portable communication device, such as a cellular telephone, that is capable of operating in a speakerphone mode. The reasons why such a device has not been successful are numerous and varied. One of the strongest reasons is that a speakerphone, by necessity, requires a more powerful audio output circuit over a conventional cellular phone. A more powerful speaker means more weight and volume, which goes against the goals of portable communication device manufactures. Furthermore, a more powerful speaker could cause a problem if placed in a conventional earpiece location since then there is the risk that a user holding the phone close to their ear, believing the phone to be in a standard mode, could be injured as the result of loud audio being played instead. Consequently, a safe approach is to use a conventional speaker for standard phone mode in the conventional location, a place the more powerful speaker elsewhere in the phone, away from the conventional earpiece location. A second reason why speakerphone implementation is difficult in a portable communication device is the close proximity between the speaker and microphone. If the dual speaker strategy suggested above is used, this is even more problematic since, in general, the portion of the phone where the microphone is located is the farthest away from the earpiece. In order for the speakerphone to sound acceptable, it must mitigate between the speaker and microphone very quickly to avoid clipping out portions of speech, or the user must get used to waiting longer than normal before speaking. To get around this problem in using mobile communications, external devices are used, coupled to the portable communication device as an accessory, that are designed very similarly to conventional land line speakerphones. However these are often worse than conventional speakerphones, depending on ambient noise levels.
Because of the obstacles recited above, and others, the design of a portable communication device operable in a speakerphone mode has proven extremely difficult. One of the key determinations to be made in providing speakerphone operation is when to activate the speaker and mute the microphone. In other words, activating the speaker only when voice information is being received, and muting the speaker otherwise. In analog cellular this is difficult because of the variance in noise, and the difficulty in signal processing to determine the presence of voice content in the received signal. Additional and expensive processing would be necessary to reliably detect voice. In digital systems, the additional processing using conventional speech processing has proven to be cumbersome, and at the least would, again, result in a significant increase in cost. Therefore, there is a need for a means by which, in a portable communication device operated in a speakerphone mode, to reliably determine when to activate the speaker and mute the microphone.